Hi! I don't know except what I've seen in my crosses and what I was told when I'd asked about that in the Naked Neck thread. It's more obvious on a NN bird. I never notice it on my bearded/muffed birds unless they drop their beards while molting, and then it's quite obvious --- but forget to ask about it.
I was told 'beard' is dominant, and bearded birds tend to have dewlap {*single gular lappet* (new term to me)} rather than proper wattles.
I hope someone that knows how it works better than I can explain it.
I have a NN Green egger hen that I hatched from Dipsy that has a single dewlap. First time I'd seen one. Thought I was seeing things. lol Now I just think she's pretty cool.